This invention relates to a control valve device for controlling the timing of start of compression of a variable capacity compressor which compresses a refrigerant gas circulating in an air-conditioning system for an automotive vehicle.
A conventional control valve device of this type is disclosed in U.S. Pat. No. 4,865,524 (corresponding to DE-OS No. 39 04 984) by the present assignee.
In this patent, as shown in FIG. 1, 1 there is disclosed a variable capacity vane compressor comprising a control element 70 disposed to rotate between the minimum capacity position and the maximum capacity position for controlling the timing of start of compression, a first pressure chamber (a low pressure chamber) 71 which is formed on one side of a pressure-receiving protuberance 70a on the control element 70 and into which is introduced suction pressure Ps as low pressure, a second pressure chamber (a high pressure chamber) 73 formed on the other side of the pressure-receiving protuberance 70a and into which is introduced discharge pressure Pd as high pressure via a restriction passage 72 to create control pressure Pc therein, and a control valve device 75 for controlling the control pressure Pc by opening and closing a passage 79 and extending between the the second pressure chamber 73 and a suction chamber 74 in response to change in the suction pressure dependent on thermal load, wherein the control element 70 is rotated in response to difference between the sum of the suction pressure Ps introduced into the first pressure chamber 71 and the urging force of a coiled spring 76 urging the control element 70 toward the minimum capacity position, and the control pressure Pc, to thereby control the capacity of the compressor.
As shown in FIGS. 1 and 2, the compressor is provided with an auxilary low-pressure chamber 78 which is separated from the suction chamber 74 by a wall 80 having a restriction through hole 77 formed therethrough and communicating the auxiliary low-pressure chamber 78 with the suction chamber 74, and bellows 75a as a pressure-responsive deformable means of the control valve device 75 is arranged within the auxiliary low-pressure chamber 78. By virtue of this construction, the suction pressure Ps is controlled such that it increases with decrease in the discharge pressure Pd as shown in FIG. 9, in order that the pressure of the refrigerant gas at the outlet of the evaporator may be substantially kept constant irrespective of change in the thermal load on the air conditioning system, thereby preventing freeze-up of the outlet of the evaporator.
More specifically, according to this variable capacity compressor, when the bellows 75a expands in response to decrease in the auxiliary low pressure Ps' to open the valve of the control valve device 75, the refrigerant gas under the control pressure Pc flows from the second pressure chamber 73 via the passage 79 into the auxiliary low-pressure chamber 78. The refrigerant gas then flows through the restriction through hole 77 into the suction chamber 74, whereby the control pressure Pc within the second pressure chamber 73 lowers to a value lower than the sum of the suction pressure Ps within the first pressure chamber 71 and the urging force of the coiled spring 76, so that the control element 70 is rotated from the maximum capacity position toward the minimum capacity position.
However, as shown in FIGS. 1 and 2, the bellows 75a is arranged within the auxiliary low-pressure chamber 78 such that when the valve becomes open, the refrigerant gas under the control pressure PC passes an end 75a.sub.1 of the bellows 75a, and a corrugated peripheral wall 75a.sub.2 of same, to the vicinity of the other end 75a.sub.3 of same to be drawn into the suction chamber 74. On this occasion, the refrigerant gas hits against the corrugated peripheral wall 75a.sub.2 to cause a slight vibration of the bellows 75a, which in turn hits against the inner peripheral wall of the auxiliary low-pressure chamber 78. This results in offensive noise, degraded capacity control of the variable capacity compressor as well as a shortened life of the bellows.